Optical power monitor

Abstract

An optical power monitor capable of being reduced in size even when designed as a multi-channel monitor, and having a reduced light transmission loss is disclosed. The optical power monitor has two optical fibers provided on the light transmission upstream and downstream sides and having cores, the end surfaces which are opposed to each other with the core optical axes offset from each other, and which are fusion-spliced to each other in a fusion splicing portion, a light reflection surface which faces a portion of the upstream-side optical fiber core end surface offset to protrude from the downstream-side optical fiber core end surface in the fusion splicing portion, and which is provided in the downstream-side optical fiber cladding layer, and a photo-diode positioned opposite from the light reflection surface with respect to the downstream-side optical fiber core. Third-order or fourth-order lights strengthening each other in lights leaked into the downstream-side optical fiber cladding layer from the upstream-side optical fiber core end surface are reflected by the reflection surface provided in the cladding layer and detected with the photo-diode.

1. An optical power monitor comprising:
 two optical fibers, each having a core in its center and a cladding layer around the core, which are disposed on an upstream side and on a downstream side of a light transmission direction, respectively, and which end surfaces face and are fusion-spliced to each other at a fusion splicing portion with their core optical axes offset from each other; 
 a light reflection surface disposed in the cladding layer of the downstream-side optical fiber, facing part of the end surface of the upstream-side optical fiber core, which is offset and protrudes from the end surface of the downstream-side optical fiber core at the fusion splicing portion, and being at an angle of 38° to 45° with the core optical axis of the downstream-side optical fiber; and 
 a photo-diode disposed opposite to the light reflection surface with respect to the downstream-side optical fiber core to detect lights that are transmitted through the upstream-side optical fiber core, leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core offset and protruding from the end surface of the downstream-side optical fiber core, and reflected by the light reflection surface, 
 wherein the light reflection surface is located at a position, that the lights leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core interfere and strengthen each other, and at a distance of 4.5 mm to 7.5 mm from the fusion splicing portion, and 
 wherein the optical fibers are curved in an arc-like shape, having a curvature radius of 0.85 m to 0.111 m or 0.347 m to 2.667 m, to rise in a direction opposite to the photo-diode and to have a peak of the arc-like shape substantially at a mid-point between the fusion splicing portion and the light reflection surface. 
 
   
   
     2. An optical power monitor as set forth in  claim 1 , wherein the offset between the core optical axes of the two optical fibers is 0.05 times to 0.32 times a core diameter of the optical fibers.